Method and apparatus for electrical control of heat transfer

ABSTRACT

A heat exchange system includes an electrode configured to electrostatically control a flow of a heated gas stream in the vicinity of a heat transfer surface and/or a heat-sensitive surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority benefit under 35 USC §119(e) toU.S. Provisional Application Ser. No. 61/294,761; entitled “METHOD ANDAPPARATUS FOR ELECTRICALLY ACTIVATED HEAT TRANSFER”, invented by DavidGoodson, Thomas S. Hartwick, and Christopher A. Wiklof, filed on Jan.13, 2010, which is currently co-pending herewith, and which, to theextent not inconsistent with the disclosure herein, incorporated byreference.

BACKGROUND

Typical external combustion systems such as combustors and boilers mayinclude relatively complicated systems to maximize the extraction ofheat from a heated gas stream. Generally, such systems may rely onforced or natural convection to transfer heat from the heated gas streamthrough heat transfer surfaces to heat sinks.

Other systems, which may include the combustion systems indicated above,or may include other systems such as turbo-jet engines, ram- orscram-jet engines, and rocket engines, for example, are limited withrespect to combustion temperature or reliability due to erosion ofcritical parts by hot gases. It would be desirable to reduce heattransfer to temperature-sensitive surfaces of such systems.

SUMMARY

According to an embodiment, a system for electrically stimulated heattransfer may include at least one first electrode positioned adjacent toa heated gas stream, and at least one heat transfer surface positionednear the at least one electrode. The heated gas stream may includepositively and/or negatively charged species evolved from a combustionreaction. At least one first electrode may be electrically modulated toattract the positively and/or negatively charged species toward the atleast one heat transfer surface. The attracted charged species mayentrain heat-bearing non-charged species. The flow of heat-bearingcharged and non-charged species may responsively flow near the at leastone heat transfer surface and transfer heat energy from the heated gasstream to a heat sink corresponding to the at least one heat transfersurface.

According to another embodiment, at least one second electrode mayselectively remove one or more charged species from the heated gasstream. The heated gas stream may thus exhibit a charge imbalance thatmay be maintained as the heated gas stream flows in the vicinity of theat least one first electrode.

According to another embodiment a heat transfer surface may include anintegrated electrode configured for electrostatic attraction of chargedspecies in a heated gas stream. The attracted charged species mayentrain heated non-charged species. The integrated electrode may beelectrically isolated from the heat transfer surface.

According to another embodiment, a method for stimulating heat transfermay include providing a heated gas carrying electrically chargedspecies, modulating a first electrode to drive the heated gas to flowadjacent to a heat transfer surface, and transferring heat from the gasto the heat transfer surface.

According to another embodiment, a method for protecting atemperature-sensitive surface may include providing a heated gascarrying electrically charged species and modulating a first electrodeto drive the heated gas to flow distal from a temperature-sensitivesurface to reduce the transfer of heat from the gas to thetemperature-sensitive surface.

According to another embodiment, an apparatus for reducing heat transferfrom a combustion reaction may include a temperature-sensitive surfacepositioned in a hot gas stream including electrically charged speciesfrom a combustion reaction and a first electrode configured to bemodulated to drive the electrically charged species from the combustionreaction to a location away from the temperature-sensitive surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a system configured to stimulate heat transfer toa heat transfer surface using an electric field, according to anembodiment.

FIG. 2 is a diagram of a system having alternative electrode arrangementcompared to the system of FIG. 1, according to an embodiment.

FIG. 3 is a partial cross section of an integrated electrode and heattransfer surface corresponding to FIG. 2, according to an embodiment.

FIG. 4 is a waveform diagram showing illustrative waveforms for drivingelectrodes of FIGS. 1-3, according to an embodiment.

FIG. 5 is a diagram of a system configured with a plurality ofelectrodes and heat transfer surfaces, according to an embodiment.

FIG. 6 is a close-up sectional view of a heat transfer surfaceillustrating an effect of impinging charged species on a boundary layer,according to an embodiment.

FIG. 7 is a diagram of a system configured to protect a heat-sensitivesurface from heat transfer using an electric field, according to anembodiment.

FIG. 8 is a diagram of a system configured to protect a heat-sensitivesurface from heat transfer using an electric field, according to anotherembodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof. In the drawings,similar symbols typically identify similar components, unless contextdictates otherwise. The illustrative embodiments described in thedetailed description, drawings, and claims are not meant to be limiting.Other embodiments may be utilized, and other changes may be made,without departing from the spirit or scope of the subject matterpresented here.

FIG. 1 is a diagram of a system 101 configured to stimulate heattransfer to a heat transfer surface 114 using an electric field,according to an embodiment. The system 101 may typically include a flame102 supported by a burner assembly 103. A combustion reaction in theflame 102 generates a heated gas 104 (having a flow illustrated by thearrow 105) carrying electrically charged species 106, 108. Typically,the electrically charged species include positively charged species 106and negatively charged species 108.

Providing a heated gas carrying charged species 106, 108 may includeburning at least one fuel from a fuel source 118, the combustionreaction providing at least a portion of the charged species andcombustion gasses. According to some embodiments, the combustionreaction may provide substantially all the charged species 106, 108.

The charged species 106, 108 may include unburned fuel; intermediateradicals such as hydride, hydroperoxide, and hydroxyl radicals;particulates and other ash; pyrolysis products; charged gas molecules;and free electrons, for example. At various stages of combustion, themix of charged species 106, 108 may vary. As will be discussed below,some embodiments may remove a portion of the charged species 106 or 108in a first portion of the heated gas 104, leaving a charge imbalance inanother portion of the heated gas 104.

For example, one embodiment may remove a portion of negative species 108including substantially only electrons, leaving a positive chargeimbalance in the gas stream 104. Positive species 106 and remainingnegative species 108 may then be electrostatically attracted to thevicinity of a heat sink 116, resulting in a stimulation of heattransfer. Alternatively, a portion of positive species 106 may beremoved from the heated gas stream 104, leaving a negative chargeimbalance in the gas stream.

A first electrode 110 may be voltage modulated by a voltage source 112.The voltage modulation may be configured to attract a portion of thecharged species 106, here illustrated as positive. Modulating the firstelectrode may include driving the first electrode to one or morevoltages selected to attract oppositely charged species, and theattracted oppositely charged species imparting momentum transfer to theheated gas.

The momentum transfer from the electrically driven charged species 106may be regarded as entraining non-charged particles, unburned fuel, ash,etc. carrying heat. The modulated first electrode 110 may be configuredto attract the charged species and other entrained species carrying heatto preferentially flow adjacent to a heat transfer surface 114. As theheat-carrying species flow adjacent to the heat transfer surface 114, aportion of the heat carried by the species is transferred through theheat transfer surface 114 to a heat sink 116.

According to an embodiment, the first electrode 110 may be arranged nearthe heat transfer surface 114. A nominal mass flow 105 may becharacterized by a velocity (including speed and direction). The firstelectrode 110 may be configured to impart a drift velocity to thecharged species 106 at an angle to the nominal mass flow velocity 105and toward the heat transfer surface 114.

As mentioned above, the system 101 may further modulate at least onesecond electrode 120 to remove a portion of the charged species 106,108. According to an embodiment, the second electrode 120 maypreferentially purge negatively-charged species 108 from the heated gas104. According to an embodiment, the second electrode may preferentiallypurge a portion of electrons 108 from the heated gas 104.

According to an embodiment, the at least one second electrode 120includes a burner assembly 103 that supports a flame 102, the flame 102providing a locus for the combustion reaction. The second electrode 120may be driven with a waveform from the voltage source 112.Alternatively, the second electrode may be driven from another voltagesource.

While the flame 102 is illustrated in a shape typical of a diffusionflame, other combustion reaction distributions may be provided,depending upon a given embodiment.

FIG. 2 is a diagram of a system 201 having alternative electrodearrangement compared to the system 101 of FIG. 1, according to anembodiment. The system 201 may include a first electrode 110 that isintegrated with the heat transfer surface 114. The system 201 mayadditionally or alternatively include an optional second electrode 120that is separate from the burner assembly 103. As with the system 101 ofFIG. 1, the burner assembly 103 is configured to support a flame 102that provides a locus for combustion and generation of at least aportion of the charged particles 106, 108 carried in the heated gas 104.

A heat sink 116 may be positioned in the heated gas stream 104 asillustrated. As the heated gas stream flows past the heat sink 116, theflow may split, as illustrated by the arrows 105. According to anembodiment, at least one electrode 110, here illustrated as beingintegrated with the heat transfer surface 114 adjoining the heat sink116, may be modulated to electrostatically attract charged species 106and/or 108. As may be appreciated, such attraction may tend to move thecharged species 106, 108 along paths at angles to the mean gas flowvelocity 105.

One possible outcome of carrying positive 106 and negative 108 speciesthrough the entirety of the heated gas stream 104 is recombination,whereby a positive charge 106 combines with a negative charge 108 toproduce one or more neutral species (not shown). Such recombination mayreduce the coupling efficiency between the first electrode 110 and theheated gas 104 by reducing the concentration of charged species 106responsive to a voltage on the first electrode 110.

As with the description corresponding to FIG. 1, the placement of apositive species attractive electrode (e.g. the first electrode 110) andnegative species attractive electrode (e.g. the second electrode 120)represents an embodiment. Other embodiments may reverse the relationshipand/or otherwise modify the embodiment of FIG. 2 without departing fromthe spirit or scope of this description.

According to the embodiment 201, the at least one second electrode 120includes an electrode positioned at a location nearer the burnerassembly 103 than the distance between the burner assembly 103 and theheat transfer surface 114. For example, the at least one secondelectrode 120 may be positioned and driven to sweep electrons 108 out ofthe flow of the heated gas 104. The modulation of the at least onesecond electrode 120 may include providing an alternating voltage. Thevoltage to which the voltage driver 112 drives the second electrode 120may attract the electrons 108 to the surface of the second electrode120. The electrons 108 may combine with a positively charged conductorincluding the at least one second electrode 120 and thus be removed fromthe heated gas stream 104.

While the open cylindrical or toric shape of the second electrode 120represents one embodiment, alternative shapes may be appropriate foralternative embodiments.

In the embodiment 201, the heat transfer surface 114 includes the firstelectrode 110. FIG. 3 is a partial cross section of an apparatus 301including an integrated electrode 110 and heat transfer surface 114corresponding to FIG. 2, according to an embodiment.

According to an embodiment, the integrated apparatus 301 may form atleast a portion of a wall of a fire tube or water tube boiler, forexample. For example, the heat transfer surface 114 may include a tubeor pipe wall that includes an opposing surface 302 abutting a heat sink116. The heat sink 116 may include a flowing liquid, vapor, and/orsteam. Alternatively, the heat transfer surface may separate a heatedgas stream 104 from a convective or forced air heat sink 116, such as inan air-to-air heat exchanger. According to another embodiment, the heatsink 116 may represent a solid heat conductor, a heat pipe, or otherapparatus that is configured to be heated by the heated gas 104.According to some embodiments, the heat transfer surface may include thesurface of a heat sink 116 that is substantially solid of a heatconductor, and there may be substantially no opposite wall 302. In someembodiments, such as in the case of a fire tube boiler embodiment forexample, the radius depicted in FIG. 3 may be flattened or reversed.

According to some embodiments, it may be desirable to provide anapparatus 301 including an integrated electrode 110 and heat transfersurface 114 wherein the electrode 110 is electrically isolated from theheat transfer surface 114. The embodiment 301 may include a thermallyconductive wall extending from the heat transfer surface 114. Thethermally conductive wall may extend to an opposite surface 302 or mayextend to an extension of the heat transfer surface 114 (such as in acylindrical heat sink 116) or may extend to an opposite surface that isdiscontinuous from the heat transfer surface 114, but which isadiabatic.

An electrical insulator 304 may be disposed over at least a portion ofthe thermally conductive wall extending from the heat transfer surface114. The first electrode 110 may include an electrically conductivelayer disposed over at least a portion of the electrical insulator 304.

Various electrical insulators 302 may be used. According to embodiments,the electrical insulator 302 may be selected for a relatively highdielectric constant (at least at a modulation frequency of the fistelectrode 110), a melting point or glass transition temperature highenough to avoid degradation, a relatively high thermal conductivity, arelatively low coefficient of thermal expansion, and/or a coefficient ofthermal expansion that is relatively well-matched to that of thematerial in the wall extending from the heat transfer surface 114 and/orthe electrode layer 110. For example, the electrical insulator 304 mayinclude one or more of polyether-ether-ketone, polyimide, silicondioxide, silica glass, alumina, silicon, titanium dioxide, strontiumtitanate, barium strontium titanate, or barium titanate. Lowerdielectric materials such as polyimide, polyether-ether-ketone, silicondioxide, silica glass, or silicon may be most appropriate for theinsulation layer for embodiments using lower voltages and/or greaterinsulator thicknesses.

According to embodiments, the conductive layer of the electrode 110 maybe selected to have relatively high conductivity and relatively highmelting point. For example, the first electrode 110 may include one ormore of graphite, chromium, an alloy including chromium, an alloyincluding molybdenum, tungsten, an alloy including tungsten, tantalum,an alloy including tantalum, or niobium-doped strontium titanate.

According to some embodiments, the at least one electrode 110 mayinclude a portion that is deposited prior to operation, e.g. a metal,crystal, or graphite, and a portion that is deposited during operation,for example carbon particles such as conductive soot or conductive ash.A useful dynamic may occur when a portion of the conductivity of the atleast one electrode 110 accrues from a deposit formed during operation.Electrodes or electrode regions that exhibit increased couplingefficiency, for example owing to system geometry, power output,stoichiometry, and/or fuel flow/heated air flow rate, may tend toattract a relatively greater particle impingement. The relativelygreater particle impingement may tend to erode or displace the depositedmatter. The removal of the deposited matter that forms a portion of theelectrode may result in a decrease in coupling efficiency to the heatedgas 104. The resultant decrease in coupling efficiency may reduce theamount of particle impingement, and hence erosion. According to anembodiment, these effects may help to provide a pseudo-equilibrium thatmay equalize “pull” on charged particles across the extent of anelectrode or across an array of electrodes.

Referring back to FIGS. 1 and 2, the voltage source 112 may beconfigured to drive the at least one first electrode 110, and optionallyat least one second electrode 120 with electrical waveforms. Asindicated above, modulating the at least one first electrode 110 mayinclude driving the first electrode 110 to one or more voltages selectedto attract oppositely charged species 106, 108, and the attractedoppositely charged species may then impart momentum transfer to theheated gas. An optional at least one second electrode 120 may be drivenwith a waveform selected to at least partially sweep some of the chargedspecies 106, 108, such as electrons 108, out of the flow of the heatedgas 104. The electrical waveforms that drive the at least one firstelectrode 110 and the optional at least one second electrode 120 mayinclude a dc voltage waveform, an ac voltage waveform, an ac voltagewith dc bias, non-periodic fluctuating waveforms, and/or combinationsthereof.

FIG. 4 is a waveform diagram 401 showing illustrative waveforms fordriving electrodes 110, 120 of FIGS. 1-3, according to an embodiment.The waveform 402 depicts an illustrative approach to driving the atleast one first electrode 110. For multiple electrode 110 systems, acommon waveform 402 may drive all the electrodes 110. Alternatively, oneor more of the multiple electrodes 110 may be driven by a waveform 402different from other waveforms 402 used to drive the other multipleelectrodes 110.

According to an embodiment, the waveform 402 may modulate between a highvoltage V_(H) and a low voltage V_(L) in a pattern characterized by aperiod P₁. The high voltage V_(H) and low voltage V_(L) may be selectedas equal magnitude variations above and below a mean voltage V₀₁. Themean voltage V₀₁ may be a ground voltage or may be a constant orvariable voltage V₀₁ representing a dc bias from ground. The absolutevalue |V_(H)−V₀₁|=|V_(L)−V₀₁| may be greater than, less than, or aboutequal to the absolute value |V₀₁|. In other words, the high voltageV_(H) may be above, about equal to, or below ground, depending on theembodiment. Similarly, the low voltage V_(L) may be above, about equalto, or below ground, depending on the embodiment.

The period P₁ includes a duration t_(L) corresponding to the low voltageV_(L) and another duration t_(H) corresponding to the high voltageV_(H). According to some embodiments t_(L)+t_(H)=P₁. According to otherembodiments (not shown), the period may include a portion of time duringwhich the voltage may be held at the mean voltage V₀₁, to yieldt_(L)+t_(H)<P₁. For embodiments where V_(L) is below ground, a positivespecies duty cycle D+ may be defined as D+=t_(L)/(t_(L)+t_(H)).Similarly, for embodiments where V_(H) is above ground, a negativespecies duty cycle D− may be defined as D−=t_(H)/(t_(L)+t_(H)). For asingle electrode 110, the positive species duty cycle D+ and thenegative species duty cycle D− are not linearly independent. However,linearly independent positive species and negative species duty cycles,D+, D− may be provided by spatially separated electrodes 110.

For the embodiments 110, 210 illustrated in FIGS. 1 and 2, and assumingconstant V_(L)<0 and constant V_(H)>0, effects of a waveform 402 will bedescribed. During period P₁ portions t_(L), the electrode 110 providesan electrostatic attraction to positive species 106 in the heated gasstream 104 and imparts a drift velocity on the positive species 106toward the electrode 110. The drift velocity may be at an angle to themass flow velocity 105 when the electrode 110 is positioned lateral tothe mass flow velocity 105. During portions t_(L), the electrode 110 maytend to repel negative species 108 entrained within the heated gasstream 104.

During period P₁ portions t_(H), the electrode 110 provides anelectrostatic attraction to negative species 108 in the heated gasstream 104 and imparts a drift velocity on the negative species 108toward the electrode 110. The drift velocity may be at an angle to themass flow velocity 105 when the electrode 110 is positioned lateral tothe mass flow velocity 105. During portions t_(H), the electrode 110 maytend to repel positive species 106 entrained within the heated gasstream 104.

For a substantially constant V_(L), a larger positive species duty cycleD+ provides a greater amount of positive species 106 attraction and alower positive species duty cycle D+ provides a lesser amount ofpositive species 106 attraction. The positive species duty cycle D+provided by the voltage source 112 may be varied according to the amountof drift momentum desired to be impressed upon the heated gas stream104. For example, at a higher flow rate 105, a higher positive speciesduty cycle D+ may be useful for maximizing positive species 106 flux,and hence maximizing heat extraction from the heated gas 104.

Similarly, for a substantially constant V_(H), a larger negative speciesduty cycle D− provides a greater amount of negative species 108attraction, and a lower negative species duty cycle D− provides a lesseramount of negative species 108 attraction. The negative species dutycycle D− provided by the voltage source 112 may be varied according tothe amount of drift momentum desired to be impressed upon the heated gasstream 104. For example, at a higher flow rate 105, a higher negativespecies duty cycle D− may be useful for maximizing negative species 108flux, hence maximizing heat extraction from the heated gas 104.

The period P₁ may be selected according to a range of considerations.For example, the concentration of positive and/or negative species 106,108 in the heated gas stream may at least partly determine an effectiveimpedance and/or conductivity related to an effective relativedielectric constant, which may, in turn, affect a frequency-dependenceof the electrostatic coupling efficiency to the heated gas 104.According to another example, the mass/charge ratio of the positiveand/or negative species may affect their frequency dependent momentumresponse to the waveform 402. Other things being equal, larger period P₁may provide higher electrostatic coupling efficiency to more massivespecies 106, 108. A shorter period P₁, on the other hand, may beadvantageous for avoiding arcing, especially when voltages V_(H) and/orV_(L) have large absolute magnitudes relative to grounded surfacesabutting the heated gas 104.

Depending on the mix of positive species 106 and negative species 108 inthe vicinity of the at least one electrode 110 and the heat transfersurface 114, one or the other of the positive species duty cycle D+ orthe negative species duty cycle D− may be of greater importance forincreasing the heat flux to the heat transfer surface 114. As describedabove, at least one second electrode 120, which may be positioned nearerthe burner assembly 103 and combustion locus 102 than the at least onefirst electrode 110, may be used to purge a portion of charged species106 or 108 from the heated gas 104. Purging a portion of the chargedspecies 106 or 108 from the heated gas 104 may tend to reduce chargerecombination and corresponding reduction in charged species 106 or 108present while the heated gas traverses a region in the vicinity of theat least one first electrode 110 and heat transfer surface 114.Additionally, purging a portion of charged species 106 or 108 may resultin a charge imbalance in the vicinity of the at least one electrode 110and the heat transfer surface 114. The charge imbalance may be used toadvantage by preferentially attracting the higher concentration species.

For example, electrons 108 may be swept out of the heated gas 104 by atleast one second electrode 120. Returning again to FIG. 4, waveform 404illustrates a waveform that may be provided by the voltage source 112 tothe at least one second electrode 120 to sweep one or more chargedspecies out of the heated air column 104. For example, the at least onesecond electrode may sweep electrons out of the gas stream 104,resulting in a positive charge imbalance in the vicinity of the at leastone first electrode 110 and the heat transfer surface 114. The electronsmay combine with a positively charged conductor including the at leastone second electrode 120 and thereafter be conducted away to the voltagesource 112.

According to an embodiment, the waveform 404 may modulate between a highvoltage V_(H2) and a low voltage V_(L2) in a pattern characterized by aperiod P₂. The high voltage V_(H2) and low voltage V_(L2) may beselected as equal magnitude variations above and below a mean voltageV₀₂. The mean voltage V₀₂ may be a ground voltage or may be a constantor variable voltage V₀₂ representing a dc bias from ground. The absolutevalue |V_(H2)−V₀₂|=|V_(L2)−V₀₂| may be greater than, less than, or aboutequal to the absolute value |V₀₂|. In other words, the high voltageV_(H2) may be above, about equal to, or below ground, depending on theembodiment. Similarly, the low voltage V_(L2) may be above, about equalto, or below ground, depending on the embodiment.

The period P₂ includes a duration t_(L2) corresponding to the lowvoltage V_(L2) and another duration t_(H2) corresponding to the highvoltage V_(H2). According to some embodiments t_(L2)+t_(H2)=P₂.According to other embodiments (not shown), the period may include aportion of time during which the voltage may be held at the mean voltageV₀₂, to yield t_(L2) +t_(H2) <P₂. For embodiments where V_(L2) is belowground, a positive species duty cycle D+₂ may be defined asD+₂=t_(L2)/(t_(L2)+t_(H2)). Similarly, for embodiments where V_(H2) isabove ground, a negative species duty cycle D−₂ may be defined asD−₂=t_(H2)/(t_(L2)t_(H2)). For a single electrode 120, the positivespecies duty cycle D+₂ and the negative species duty cycle D−₂ are notlinearly independent. However, linearly independent positive species andnegative species duty cycles, D+₂, D−₂ may be provided by spatiallyseparated electrodes 120.

For the embodiments 110, 210 illustrated in FIGS. 1 and 2, and assumingconstant V_(L2)<0 and constant V_(H2)>0, effects of a waveform 404 willbe described. During period P₂ portions t_(L2), the electrode 120provides an electrostatic attraction to positive species 106 in theheated gas stream 104 and imparts a drift velocity on the positivespecies 106 toward the electrode 120. The drift velocity may be at anangle to the mass flow velocity 105 when the electrode 120 is positionedlateral to the mass flow velocity 105. During portions t_(L2), theelectrode 120 may tend to repel negative species 108 entrained withinthe heated gas stream 104.

During period P₂ portions t_(H2), the electrode 120 provides anelectrostatic attraction to negative species 108 in the heated gasstream 104 and imparts a drift velocity on the negative species 108toward the electrode 120. The drift velocity may be at an angle to themass flow velocity 105 when the electrode 120 is positioned lateral tothe mass flow velocity 105. During portions t_(H2), the electrode 120may tend to repel positive species 106 entrained within the heated gasstream 104.

For a substantially constant V_(L2), a larger positive species dutycycle D+₂ provides a greater amount of positive species 106 attractionand a lower positive species duty cycle D+₂ provides a lesser amount ofpositive species 106 attraction. The positive species duty cycle D+₂provided by the voltage source 112 may be varied according to the amountof positive species 106 desired to be removed from the heated gas stream104. For example, at a higher flow rate 105, a higher positive speciesduty cycle D+₂ may be useful for maximizing positive species 106 flux,and hence maximizing the withdrawal of positive species from the heatedgas 104.

Similarly, for a substantially constant V_(H2), a larger negativespecies duty cycle D−₂ provides a greater amount of negative species 108attraction, and a lower negative species duty cycle D−₂ provides alesser amount of negative species 108 attraction. The negative speciesduty cycle D−₂ provided by the voltage source 112 may be variedaccording to the amount of negative species to be removed from theheated gas stream 104. For example, at a higher flow rate 105, a highernegative species duty cycle D−₂ may be useful for maximizing negativespecies 108 flux, hence maximizing negative species extraction from theheated gas 104.

The period P₂ may be selected according to a range of considerations.For example, the concentration of positive and/or negative species 106,108 in the heated gas stream may at least partly determine an effectiveimpedance and/or conductivity related to an effective relativedielectric constant, which may, in turn, affect a frequency-dependenceof the electrostatic coupling efficiency to the heated gas 104.According to another example, the mass/charge ratio of the positiveand/or negative species may affect their frequency dependent momentumresponse to the waveform 404. Other things being equal, larger period P₂may provide higher electrostatic coupling efficiency to more massivespecies 106, 108. A shorter period P₂, on the other hand, may beadvantageous for avoiding arcing or avoiding the undesirable removal ofmove massive charged species 106, 108, especially when voltages V_(H2)and/or V_(L2) have large absolute magnitudes relative to groundedsurfaces abutting the heated gas 104.

According to an illustrative embodiment, at least one second electrode120 may be configured to sweep a portion of electrons from the heatedgas 104, but avoid sweeping other negative species from the heated gas104. For example, the period P₂ of the second electrode modulation maybe selected to impart sufficient momentum on electrons to withdraw aportion of the free electrons. More massive negative particles respond(accelerate) more slowly to the force imparted by the electrical fieldbecause of the inverse mass relationship between force and acceleration.Hence, a relatively short period P₂ may result in an acceleration ofelectrons to the surface of the second electrode, but leave more massivenegative species in the heated gas 104.

At least one first electrode 110 may be configured to primarily driveremaining and relatively massive positive species including unburnedfuel and ash toward a heat transfer surface 114. For example, for asystem including a 7.6 cm diameter tube enclosing the heated volume anda heated gas 104 velocity of about 90 cm/second, the at least one firstelectrode 110 may be modulated between about 0 volts and −10,000 voltsat a frequency of about 300 Hz at a 97% duty cycle. This results in theat least one first electrode 110 being periodically modulated to −10 kVfor 3.22 milliseconds and then to 0V for 0.1 milliseconds, for a totalperiod of 3.32 milliseconds (301.2 Hz).

According to an embodiment, the at least one first electrode 110 mayproduce an electric field strength of about 1 kV/cm. Because of thelarge number of collisions between species in the heated gas 104,acceleration may be ignored and moderate mass positively charged species106 (e.g. CO⁺, C₃H₈ ⁺, etc.) in the stream (along with entrained gas andparticles) may be approximated to be imparted with a nominal driftvelocity toward the first electrode 110 (and hence the heat transfersurface 114) of about 1000 cm/second. In comparison to an embodimenthaving a typical gas flow rate of about 100 cm/second, one mayappreciate that driving the at least one first electrode 110 maysignificantly affect the transfer of heat through the heat transfersurface 114.

At least one second electrode 120 may be configured to primarily driveelectrons out of the heated gas 104. For example for a system using aburner nozzle as the second electrode 120 centered in a 7.6 cm diametertube and a heated gas velocity of about 90 cm/second, the secondelectrode 120 may be modulated between about 0 volts and +10,000 voltsat a frequency of about 300 Hz at a 97% duty cycle. This results in theat least one second electrode 120 being periodically modulated to +10 kVfor 3.22 milliseconds and then to 0V for 0.1 milliseconds, for a totalperiod of 3.32 milliseconds (301.2 Hz). Another second electrode 120modulation schema may provide 50% duty cycle modulation between 0V and+10,300V at a frequency of 694.4 kHz.

According to an embodiment, the at least one second electrode 120 mayproduce an electric field strength of about 1 kV/cm. Because of thelarge number of collisions between species in the heated gas 104,acceleration may be ignored and low mass negatively charged species 106(e.g. e⁻) in the stream may be approximated to be imparted with anominal drift velocity toward the second electrode 120 of about 10⁵cm/second, which is more than sufficient to overcome an illustrative gasflow rate of 100 cm/sec. However, because of the low mass of electrons,relatively little momentum is transferred to other species in the heatedgas 104, thus avoiding entrainment, and significant flow of heat to thesecond electrode 120 may be avoided.

FIG. 5 is a diagram of a system 501 configured with a plurality of firstelectrodes 110 a, 110 b and heat transfer surfaces 114 a, 114 b, 114 c,according to an embodiment. The plurality of first electrodes 110 a-band heat transfer surfaces 114 a-c may be arranged to respectively driveand receive heat transfer from a heated gas stream 104 generated by atleast one combustion locus or flame 102 supported by at least one burnerassembly 103. The at least one combustion reaction supported by the atleast one burner assembly 103 may evolve positively charged species 106and negatively charged species 108 into the heated gas stream 104.

The plurality of first electrodes may be driven with a common waveformfrom a voltage source 112 or with separate waveforms. The plurality offirst electrodes 110 a, 110 b may be configured to impart driftvelocities to the positively charged species 106 and/or the negativelycharged species 108 at a plurality of angles to a nominal mass flowvelocity 105. A heat transfer surface may include a plurality of heattransfer surfaces 114 a-c. The plurality of heat transfer surfaces 114a-c may correspond to a common heat sink or to a corresponding pluralityof heat sinks 116 a-c.

For example, a common heat sink 116 a may correspond to a water tube ina boiler. The water tube may, for example, include an electricallyinsulating layer (not shown) formed over substantially the entirety ofthe water tube. A plurality of electrodes 110 a-b may be formed aspatterned conductors over the insulating layer (not shown) on the watertube 116 a. The plurality of heat transfer surfaces 114 a-c maycorrespond to regions between the patterned electrodes 110 a-b.

According to an alternative embodiment, the plurality of heat transfersurfaces 114 a-c may correspond to a plurality of heat sinks 116 a-c.For example, at least a portion of the plurality of first electrodes 110a, 110 b may be interdigitated with at least a portion of the pluralityof heat transfer surfaces 114 a-c. The heat sinks 116 a-c and heattransfer surfaces 114 a-c may optionally be electrically conductive. Theplurality of first electrodes 110 a-b may be separated from the heattransfer surfaces 114 a-c by air gaps. The air gaps may insulate theplurality of first electrodes 110 a-b from the plurality of heattransfer surfaces 114 a-c and/or the plurality of heat sinks 116 a-c.

A plurality of heat transfer surfaces 114 a-c and correspondingplurality of heat sinks 116 a-c may form a heat sink array 502. A system501 may include a plurality of heat sink arrays 502, 502 b, 502 c. Theheat sink arrays 502, 502 b, 502 c may include electrodes driven by acommon voltage source 112, or by a corresponding plurality of voltagesources (not shown).

FIG. 6 is a close-up sectional view 601 of heat transfer surfaces 114 a,114 b illustrating an effect of impinging charged species 106, 108 (andany entrained non-charged species) on boundary layers 602 a, 602 b,according to an embodiment. A heated gas stream 104 includes a bulk flowvelocity 105. Heat transfer surfaces 114 a, 114 b may be disposedadjacent to the heated gas stream 104.

A first heat transfer surface 114 a, may not include a correspondingelectrode, or may represent a moment during which a correspondingelectrode is not modulated to attract a charged species. A boundarylayer 602 a lies over the heat transfer surface 114 a. The boundarylayer 602 a may represent a thickness of relatively quiescent air acrosswhich thermal diffusion and/or radiation may dominate as heat transfermechanisms over convective heat transfer. Even in cases where the heatedair stream 104 as a whole is moving with sufficient velocity 105 toprovide convective heat transfer, for example as turbulent flow, theboundary layer 602 a may be present. In cases where the heated airaverage velocity 105 is high enough to reach a Reynolds numbercharacteristic of turbulent flow, the boundary layer 602 a may becharacterized as a turbulent boundary layer.

Convective heat transfer and/or heat transfer between regions outsidethe boundary layer 602 a is characterized by a higher heat transfercoefficient than heat transfer across the boundary layer 602 a. Thethickness of the boundary layer 602 a may be proportional to itsresistance to heat transfer from the heated air stream 104 to the heattransfer surface 114 a.

A second heat transfer surface 114 b includes a corresponding electrode110 b that is modulated or energized to attract charged species 106 fromthe heated air stream 104. The corresponding electrode 110 b may, forexample, include a conduction path within a conductive wall defined atleast partially by the heat transfer surface 114 b. This may beparticularly appropriate when the wall is electrically isolated and liesadjacent a substantially non-conductive heat sink, as in an air-to-airheat exchanger for example. Alternatively, the corresponding electrode110 b may overlie the heat transfer surface 114 b, for example accordingto an embodiment corresponding to that of FIG. 3. Alternatively, thecorresponding electrode 110 b may be disposed near the heat transfersurface 114 b. As will be appreciated, while an electrode 110 b disposednear the heat transfer surface 114 b may not drive the charged species106 to accelerate toward the heat transfer surface, it may impartsufficient momentum to the charged species 106 (and any non-charged oroppositely-charged species entrained therewith) to cause them to impingeupon the heat transfer surface 114 b as shown diagrammatically.

Charged species 106 that impinge upon the heat transfer surface 114 bmay do so by penetrating a boundary layer 602 b. The penetration of thecharged species 106 may cause the boundary layer 602 b to be thinnerthan the boundary layer 602 a. The penetration of the charged species106 may also effectively raise the Reynolds number sufficiently tosubstantially convert a laminar boundary layer 602 a to a turbulentboundary layer 602 b. The mixing or disruption of the boundary layer 602b by the impinging charged species, any entrained non-charged species,and any entrained oppositely-charged species may result in raising aheat transfer coefficient for transfer of heat from the heated gasstream 104 through the heat transfer surface 114 b.

Additionally, a combination of charged species 106 with opposite chargecarriers in the electrode 110 b may release a heat of associationcorresponding to a lower energy state of a neutral species.Additionally, the kinetic energy of the charged species 106 (and otherentrained species) impinging on the heat transfer surface 114 b may beconverted to additional heat energy.

While the flame 102 and burner assembly 103 are depicted in FIGS. 1, 2,and 5, as resembling a gas burner and flame, various burner embodimentsare contemplated. For example, the burner assembly may include one ormore of a fluidized bed, a grate, moving grate, a pulverized coalnozzle, a gas burner, a gas nozzle, an oil burner, arrays of burnerassemblies, or other embodiments. Flames 102 may include laminar flames,other diffusion flames, premixed flames, turbulent flames, agitatedflames, stoichiometric flames, non-stoichiometric flames, orcombinations thereof.

Driving Heat Away from a Surface

While description above has focused on driving heat energy toward asurface, other embodiments can drive heat energy away from a surface.Generally, this can be accomplished by inverting either the polarity ofthe highest concentration charged species in the gas stream, by movingthe location of the electrode(s) with respect to the heat transfer (ortemperature-sensitive) surface(s), by inverting the voltage waveformapplied to the electrode(s), or by applying a (opposite sign) biasvoltage to the waveform. In most combustion systems, the highest massand highest stability charged species are positively charged. Therefore,for most practical solutions involving combustion systems, the bestoptions may involve either moving the electrode(s), substantiallyinverting the voltage waveform applied to the electrode(s), or byapplying or inverting a bias voltage to the voltage waveform.

FIG. 7 is a diagram of a system 701 configured to protect atemperature-sensitive surface 702 and/or an underlyingtemperature-sensitive structure 704 from heat transfer, according to anembodiment. The operation of the system 701 may correspond to theoperation of the system 101 shown in FIG. 1, except that the electricfield or the charged species population is inverted.

The system 701 may typically include a flame 102 supported by a burnerassembly 103. A combustion reaction in the flame 102 generates a heatedgas 104, that exhibits a mass a flow illustrated by the arrow 105,carrying electrically charged species 106, 108. Typically, theelectrically charged species include positively charged species 106 andnegatively charged species 108.

Providing a heated gas carrying charged species 106, 108 may includeburning at least one fuel from a fuel source 118, the combustionreaction providing at least a portion of the charged species andcombustion gasses. According to some embodiments, the combustionreaction may provide substantially all the charged species 106, 108.

The charged species 106, 108 may include unburned fuel; intermediateradicals such as hydride, hydroperoxide, and hydroxyl radicals;particulates and other ash; pyrolysis products; charged gas molecules;and free electrons, for example. At various stages of combustion, themix of charged species 106, 108 may vary. As will be discussed below,some embodiments may remove a portion of the charged species 106 or 108in a first portion of the heated gas 104, leaving a charge imbalance inanother portion of the heated gas 104.

For example, one embodiment may remove a portion of negative species 108including substantially only electrons, leaving a positive chargeimbalance in the gas stream 104. Positive species 106 may then beelectrostatically attracted away from the vicinity of a structure 704,resulting in reduced heat transfer across a temperature-sensitivesurface 702 of the structure 704 and to the temperature-sensitivestructure 704 itself. Alternatively, a portion of positive species 106may be removed from the heated gas stream 104, leaving a negative chargeimbalance in the gas stream. While the negative species 108 is shownwith a drift velocity toward the structure 704 and thetemperature-sensitive surface 702, the waveform applied to the voltagesource may, in fact, cause a net neutral path along the mass flow 105 ormay also drive the negatively charges species away from the structure704 with its temperature-sensitive surface. This may be done bycontrolling modulation on-off cycles and the duty cycle of the waveformin a manner corresponding to the charge/mass ratio of the negativespecies 108. Alternatively, with a low enough mass negative species 108and/or depopulation of the negative species 108, the negative species108 may impart negligible momentum upon the gas stream 104, and thus maynot result in substantial movement of heated gases toward the structure104 and temperature-sensitive surface 702.

A first electrode 110 may be voltage modulated by a voltage source 112.The voltage modulation may be configured to create a voltage potentialacross the heated gas stream 104 to drive a portion of the chargedspecies 106, here illustrated as positive, away from the structure 704and temperature-sensitive surface 702. Modulating the first electrodemay include driving the first electrode to one or more voltages selectedto, in combination with a counter electrode 706, repel oppositelycharged species, and the repelled oppositely charged species impartingmomentum transfer to the heated gas.

The momentum from the electrically driven charged species 106 may betransferred to non-charged particles, unburned fuel, ash, air, etc.carrying heat. The modulated first electrode 110 may be configured torepel the charged species and other entrained species carrying heat topreferentially flow away from a temperature-sensitive surface 702. Asthe heat-carrying species flow away from to the heat transfer surface114, a reduced portion of the heat carried by the heated gas 105 istransferred through the temperature-sensitive surface 702 to thestructure 704.

According to an embodiment, the first electrode 110 may be arranged nearthe temperature-sensitive surface 702. A nominal mass flow 105 may becharacterized by a velocity (including speed and direction). The firstelectrode 110 may be configured to impart a drift velocity to thecharged species 106 at an angle to the nominal mass flow velocity 105and away from the temperature-sensitive surface 702.

As mentioned above, the system 701 may further modulate at least onesecond electrode 120 to remove a portion of the charged species 106,108. According to an embodiment, the second electrode 120 maypreferentially purge negatively-charged species 108 from the heated gas104. According to an embodiment, the second electrode may preferentiallypurge a portion of electrons 108 from the heated gas 104.

According to an embodiment, the at least one second electrode 120 mayinclude a burner assembly 103 that supports a flame 102, the flame 102providing a locus for the combustion reaction. The second electrode 120may be driven with a waveform from the voltage source 112.Alternatively, the second electrode may be driven from another voltagesource or may be held at ground.

The counter electrode 706, which may be referred to as a third electrode(whether or not the optional second electrode is present), is shown aselectrically coupled to ground. The third electrode 706 may optionallybe formed as a grounded combustion system structure, and may thus not bean explicit structure. Optionally, the third electrode 706 may be drivenfrom the voltage source 112 (via a connection that is not shown thatreplaces the ground connection) or another voltage source (not shown)with a waveform that is opposite in sign to the waveform applied to theelectrode 110.

Optionally, the electrode 110 may be combined with the structure 704 ormay be formed on the surface of the structure 704. For example, thefirst electrode 110 may be disposed over an electrical insulator and theelectrical insulator is disposed over the temperature-sensitive surface702 or the electrode 110 may be formed from the structure 704 and/or thetemperature-sensitive surface 702. The electrical insulator may, forexample, include at least one of polyether-ether-ketone, polyimide,silicon dioxide, silica glass, alumina, silicon, titanium dioxide,strontium titanate, barium strontium titanate, or barium titanate. Thefirst electrode 110 may include at least one of graphite, chromium, analloy including chromium, an alloy including molybdenum, tungsten, analloy including tungsten, tantalum, an alloy including tantalum, orniobium-doped strontium titanate.

The structure 704 and temperature-sensitive surface 702, optionalelectrical insulator (not shown), and first electrode 110 may form atleast a portion of a wall of a fire tube or water tube boiler. Inanother example, the temperature-sensitive surface 702 and the structure704 may include a turbine blade or other structure subject todegradation by exposure to the hot gas stream 104. The temperatureprotection approaches shown herein may then be used to extend turbine(or other structure) life, improve reliability, reduce weight, and/orincrease thrust by allowing hotter combustion gases 104 withoutdegrading the temperature-sensitive structure(s) 704 and/ortemperature-sensitive surface(s) 702. The temperature-sensitive surface702 (and optionally structure 704) may include one or more of titanium,a titanium alloy, aluminum, an aluminum alloy, steel, stainless steel, acomposite material, a fiberglass and epoxy material, a Kevlar and epoxymaterial, or a carbon fiber and epoxy material.

Optionally, the electrode 110 may be positioned away from the structure704 and temperature-sensitive surface 702 to directly exert anattractive force on the majority species 106. FIG. 8 is a diagram of asystem configured to protect a temperature-sensitive surface 702 and/oran underlying temperature-sensitive structure 704 from heat transfer,according to an embodiment where the electrode 110 is positioned distalfrom the structure 704 and surface 702. The operation of the system 701may correspond to the operation of the system 101 shown in FIG. 1,except that the position of the electrode 110 is moved away from thesurface 702.

The system 801 may typically include a flame 102 supported by a burnerassembly 103. A combustion reaction in the flame 102 generates a heatedgas 104, that exhibits a mass a flow illustrated by the arrow 105,carrying electrically charged species 106, 108. Typically, theelectrically charged species include positively charged species 106 andnegatively charged species 108. Operation of the combustion portion ofthe system 801 and the optional second electrode 120 may besubstantially identical to the operation of the system 701, as describedabove.

Positive species 106 and remaining negative species 108 may then beelectrostatically attracted away from the vicinity of the structure 704,resulting in reduced heat transfer across a temperature-sensitivesurface 702 of the structure 704 and to the temperature-sensitivestructure 704 itself. Alternatively, a portion of positive species 106may be removed from the heated gas stream 104, leaving a negative chargeimbalance in the gas stream.

A first electrode 110 may be voltage modulated by a voltage source 112.The voltage modulation may be configured to create a voltage potentialacross the heated gas stream 104 to drive a portion of the chargedspecies 106, here illustrated as positive, away from the structure 704and temperature-sensitive surface 702. Modulating the first electrodemay include driving the first electrode to one or more voltages selectedto, in combination with a counter electrode 706, attract oppositelycharged species, with the attracted oppositely charged species impartingmomentum transfer to the heated gas 104. As described above, while thenegative species 108 is shown with a drift velocity toward the structure704 and the temperature-sensitive surface 702, the waveform applied tothe voltage source may, in fact, cause a net neutral path along the massflow 105 or may also drive the negatively charges species away from thestructure 704 with its temperature-sensitive surface 702.

The momentum from the electrically driven charged species 106 may betransferred to non-charged particles, unburned fuel, ash, air, etc.carrying heat. The modulated first electrode 110 may be configured toattract the charged species and other entrained species carrying heat topreferentially flow away from a temperature-sensitive surface 702. Asthe heat-carrying species flow away from to the heat-sensitive surface702, a reduced portion of the heat carried by the heated gas 105 istransferred through the temperature-sensitive surface 702 to thestructure 704.

A counter electrode 706, which may be referred to as a third electrode(whether or not the optional second electrode is present), is shown aselectrically coupled to ground. The third electrode 706 may optionallybe formed as a grounded combustion system structure, and may thus not bean explicit structure. Optionally, the third electrode 706 may be drivenfrom the voltage source 112 (via a connection that is not shown thatreplaces the ground connection) or another voltage source (not shown)with a waveform that is opposite in sign to the waveform applied to theelectrode 110.

Optionally, the electrode 706 may be combined with the structure 704 ormay be formed on the surface of the structure 704. For example, thethird electrode 706 may be disposed over an electrical insulator and theelectrical insulator is disposed over the temperature-sensitive surface702 or the third electrode 706 may be formed from the structure 704and/or the temperature-sensitive surface 702. The electrical insulatormay, for example, include at least one of polyether-ether-ketone,polyimide, silicon dioxide, silica glass, alumina, silicon, titaniumdioxide, strontium titanate, barium strontium titanate, or bariumtitanate. The third electrode 706 may include at least one of graphite,chromium, an alloy including chromium, an alloy including molybdenum,tungsten, an alloy including tungsten, tantalum, an alloy includingtantalum, or niobium-doped strontium titanate.

The structure 704 and temperature-sensitive surface 702, optionalelectrical insulator (not shown), and third electrode 706 may form atleast a portion of a wall of a fire tube or water tube boiler. Inanother example, the temperature-sensitive surface 702 and the structure704 may include a turbine blade or other structure subject todegradation by exposure to the hot gas stream 104. The temperatureprotection approaches shown herein may then be used to extend turbine(or other structure) life, improve reliability, reduce weight, and/orincrease thrust by allowing hotter combustion gases 104 withoutdegrading the temperature-sensitive structure(s) 704 and/ortemperature-sensitive surface(s) 702. The temperature-sensitive surface702 (and optionally structure 704) may include one or more of titanium,a titanium alloy, aluminum, an aluminum alloy, steel, stainless steel, acomposite material, a fiberglass and epoxy material, a Kevlar and epoxymaterial, or a carbon fiber and epoxy material.

Optionally, the approaches related to heat attraction (shown in FIG. 1and elsewhere) may be combined with the approaches related to heatprotection (shown in FIGS. 7 and 8). For example, the voltage source 112may be configured to preferentially apply heat to a heat sink 116 duringa portion of a cycle or for a period, and then preferentially removeheat from the heat sink structure 704 during another portion of thecycle or after the period is over. This may be used, for example, totemporarily apply higher thrust against a turbine blade, such as duringperiods of full military power, and then allow the turbine blades tocool in order to avoid structural failure.

While the flame 102 in FIGS. 7 and 8 is illustrated in a shape typicalof a diffusion flame, other combustion reaction distributions may beprovided, depending upon a given embodiment.

Various configurations of embodiments depicted in FIGS. 7 and 8 arecontemplated. For example, the first electrode 110 and/or the thirdelectrode 706 may either or each include a plurality of electrodesconfigured to impart drift velocities to electrically charged species ata plurality of angles to the nominal mass flow velocity. The firstelectrode 110 and/or the third electrode 706 may include a plurality offirst electrodes 110 and/or third electrodes 706, and thetemperature-sensitive surface 702 (and structure(s) 704) may include aplurality of temperature-sensitive surfaces 702 (704). At least aportion of the plurality of first electrodes 110 may then beinterdigitated with at least a portion of the plurality oftemperature-sensitive surfaces 702.

As indicated above, the voltage waveform provided by the voltage source112 may be driven as indicated elsewhere herein, typically inverted orat an opposite bias for the arrangement 701 of FIG. 7, or directly aspreviously shown for the arrangement 801 of FIG. 8. The waveform mayinclude a dc negative voltage, an ac voltage including a negativeportion, or an ac voltage on a dc negative bias voltage for thearrangement of FIG. 8. Similarly, the waveform may include a dc positivevoltage, an ac voltage including a positive portion, or an ac voltage ona dc positive bias voltage for the arrangement of FIG. 7.

The descriptions and figures presented herein are necessarily simplifiedto foster ease of understanding. Other embodiments and approaches may bewithin the scope of inventions described herein. Inventions describedherein shall be limited only according to the appended claims, whichshall be accorded their broadest valid meaning.

1. A method for stimulating heat transfer, comprising: providing aheated gas carrying electrically charged species; temporally modulatinga first electrode to create an electric field to drive the heated gas toflow adjacent to a heat transfer surface; and transferring heat from thegas to the heat transfer surface.
 2. The method for stimulating heattransfer of claim 1, wherein temporally modulating the first electrodeto drive the heated gas includes driving the first electrode to one ormore voltages selected to attract oppositely charged species, and theattracted oppositely charged species imparting momentum transfer to theheated gas.
 3. The method for stimulating heat transfer of claim 1,wherein providing a heated gas carrying charged species includes burningat least one fuel, the combustion reaction providing at least a portionof the charged species.
 4. The method for stimulating heat transfer ofclaim 3, wherein the combustion reaction provides substantially all thecharged species.
 5. The method for stimulating heat transfer of claim 1,further comprising temporally modulating at least one second electrodeto preferentially purge electrons from the heated gas.
 6. The method forstimulating heat transfer of claim 5, wherein the at least one secondelectrode includes a burner assembly.
 7. The method for stimulating heattransfer of claim 5, wherein providing a heated gas carrying ionizedspecies includes supporting a flame with a burner assembly; and whereinthe at least one second electrode includes an electrode positioned at alocation nearer the burner assembly than the distance between the burnerassembly and the heat transfer surface.
 8. The method for stimulatingheat transfer of claim 5, wherein the at least one second electrode ispositioned to sweep electrons out of the flow of the heated gas.
 9. Themethod for stimulating heat transfer of claim 5, wherein the temporalmodulation of the at least one second electrode includes providing analternating voltage configured to drive the electrons to combine with apositively charged conductor including the at least one secondelectrode.
 10. The method for stimulating heat transfer of claim 5,wherein the at least one second electrode is modulated between a rangeof positive voltages at a frequency of about 200 Hz or more.
 11. Themethod for stimulating heat transfer of claim 10, wherein the at leastone second electrode is modulated at a frequency of about 300 Hz ormore.
 12. The method for stimulating heat transfer of claim 10, whereinthe range of positive voltages includes about 0 volts to +500 volts ormore.
 13. The method for stimulating heat transfer of claim 12, whereinthe range of positive voltages includes about 0 volts to +10 KV or more.14. (canceled)
 15. The method for stimulating heat transfer of claim 14,wherein temporally modulating the first electrode includes modulatingthe first electrode at a frequency of about 500 Hz or less.
 16. Themethod for stimulating heat transfer of claim 1, wherein the heated gascarrying electrically charged species includes combustion gasses. 17.The method for stimulating heat transfer of claim 1, wherein the heattransfer surface includes the first electrode.
 18. The method forstimulating heat transfer of claim 17, wherein the heat transfer surfaceincludes: a thermally conductive wall; an electrical insulator disposedover at least a portion of the thermally conductive wall; and the firstelectrode including an electrically conductive layer disposed over theelectrical insulator. 19.-33. (canceled)
 34. A method for protecting atemperature-sensitive surface, comprising: providing a heated gascarrying electrically charged species; and temporally modulating a firstelectrode to form an electric; field to drive the heated gas to flowdistal from a temperature-sensitive surface to reduce the transfer ofheat from the gas to the temperature-sensitive surface.
 35. The methodfor protecting a temperature-sensitive surface of claim 34, whereintemporally modulating the first electrode to drive the heated gasincludes driving the first electrode to one or more voltages selected toattract oppositely charged species, and the attracted oppositely chargedspecies imparting momentum transfer to the heated gas.
 36. The methodfor protecting a temperature-sensitive surface of claim 34, whereinproviding a heated gas carrying charged species includes burning atleast one fuel, the combustion reaction providing at least a portion ofthe charged species.
 37. The method for protecting atemperature-sensitive surface of claim 36, wherein the combustionreaction provides substantially all the charged species.
 38. The methodfor protecting a temperature-sensitive surface of claim 34, furthercomprising temporally modulating at least one second electrode topreferentially purge electrons from the heated gas.
 39. The method forprotecting a temperature-sensitive surface of claim 38, wherein the atleast one second electrode includes a burner assembly.
 40. The methodfor protecting a temperature-sensitive surface of claim 38, whereinproviding a heated gas carrying ionized species includes supporting aflame with a burner assembly; and wherein the at least one secondelectrode includes an electrode positioned at a location nearer theburner assembly than the distance between the burner assembly and thetemperature-sensitive surface.
 41. The method for protecting atemperature-sensitive surface of claim 38, wherein the at least onesecond electrode is positioned to sweep electrons out of the flow of theheated gas.
 42. The method for protecting a temperature-sensitivesurface of claim 38, wherein the temporal modulation of the at least onesecond electrode includes providing an alternating voltage configured todrive the electrons to combine with a positively charged conductorincluding the at least one second electrode.
 43. The method forprotecting a temperature-sensitive surface of claim 38, wherein the atleast one second electrode is temporally modulated between a range ofpositive voltages at a frequency of about 200 Hz or more.
 44. The methodfor protecting a temperature-sensitive surface of claim 43, wherein theat least one second electrode is modulated at a frequency of about 300Hz or more.
 45. The method for protecting a temperature-sensitivesurface of claim 43, wherein the range of positive voltages includesabout 0 volts to +500 volts or more.
 46. The method for protecting atemperature-sensitive surface of claim 45, wherein the range of positivevoltages includes about 0 volts to +10 KV or more.
 47. The method forprotecting a temperature-sensitive surface of claim 38, whereintemporally modulating the first electrode includes modulating the firstelectrode between a range of negative voltages.
 48. The method forprotecting a temperature-sensitive surface of claim 47, whereintemporally modulating the first electrode includes modulating the firstelectrode at a frequency of about 500 Hz or less.
 49. The method forprotecting a temperature-sensitive surface of claim 34, wherein theheated gas carrying electrically charged species includes combustiongases.
 50. The method for protecting a temperature-sensitive surface ofclaim 34, wherein the heat-sensitive surface includes the firstelectrode.
 51. The method for protecting a temperature-sensitive surfaceof claim 50, wherein the temperature-sensitive surface includes: a wall;an electrical insulator disposed over at least a portion of the wall;and the first electrode including an electrically conductive layerdisposed over the electrical insulator. 52.-73. (canceled)